Context & scale
After 40 years, crystalline silicon (c-Si) solar cells remain the clear leaders of the terrestrial photovoltaic market. This position is largely due to continual adjustments of the c-Si cell architecture, which have provided steady efficiency gains, together with drastic cost reductions brought about by large-scale manufacturing. To maintain forward momentum and lift the industry average power conversion efficiency to ∼ 25%, the next major change to take place is the integration of“passivated contacts,” which address the losses implicit to the metal-silicon contacts used in today’s cells. Recent years have seen increased investment and rapid improvement in a few passivated contact technologies. The decision of when and which passivated contact scheme to adopt is not straightforward, requiring consideration of factors beyond the standard cost-to-performance ratio, such as ultimate efficiency potential as well as capital and retraining expenditure. This perspective focuses on one stream of future c-Si solar cells incorporating passivated contacts based on doped polycrystalline silicon/SiO 2 junctions, commonly called poly-Si junctions.
Summary
Despite the maturity of crystalline silicon photovoltaics (c-Si PV), the last 6 years have seen a string of efficiency improvements, most of which are centered around reducing the losses related to the directly metallized, heavily doped regions found in conventional c-Si solar cells. Among these advancements, polysilicon (poly-Si) passivated junctions, formed by embedding a thin silicon oxide (SiO 2 ) layer between the c-Si wafer and a highly doped poly-Si layer, are emerging as one of the most promising alternatives, and efficiencies above 26% have already been demonstrated. The excellent performance of this junction architecture has been found to be remarkably independent of the deposition and/or doping technique used—even extending to techniques already prevalent in industry. This greatly reduces the capital and retraining expenditure needed to integrate the new technology into mainstream production lines, allowing it to be an evolutionary, rather than disruptive advancement. This has led to the rapid demonstration of large-area cells featuring poly-Si contacts by multiple PV manufacturing companies, with efficiencies above 24.5%. Although a bright future for poly-Si junctions is anticipated, as supported by the predictions of the International Technology Roadmap of Photovoltaics, several issues remain to be resolved, including those associated with the cost of and damage to the poly-Si layers due to the cell’s metallization
